Flash memory array with internal refresh

Abstract

In a flash memory array, an internal refresh periodically rewrites the information stored in each of the rows of memory cells in a flash memory. The flash memory array includes a refresh pointer bitline that indicates the row to be refreshed. In a first embodiment of the present invention, the internal refresh is performed automatically after every user erase/program cycle. In second and third embodiments, the user of the of the flash memory array selects when the internal refresh is performed, but the address of the row to be refreshed is supplied internally. In each of the three the embodiments, the internal refresh includes the four operations of SCAN, REFRESH ERASE, REFRESH PROGRAM, and INCREMENT.

What is claimed is: 
     
       1. A method of operating a flash memory array comprising: scanning said flash memory array for a row to be refreshed;   erasing said row to be refreshed in said flash memory array;   programming said row to be refreshed in said flash memory array; and   incrementing an address of said row to be refreshed in said flash memory array.   
     
     
       2. A method of operating a flash memory array as in claim 1, further including: erasing a selected row in said flash memory array; and   programming said selected row in said flash memory array.   
     
     
       3. A method of operating a flash memory array as in claim 2, wherein said erasing a selected row and said programming said selected row are performed prior to said scanning. 
     
     
       4. A method of operating a flash memory array as in claim 2, wherein said erasing a selected row and said programming said selected row are performed between said scanning and said erasing said row. 
     
     
       5. A method of operating a flash memory array comprising: reading a selected row in said flash memory array and storing a state of a selected bit in said flash memory array;   erasing said selected row is said flash memory array;   programming said selected row in said flash memory array; and   programming said selected bit to a first state when said state of said selected bit stored in said reading and storing act is in a said first state.   
     
     
       6. A method of operating a flash memory array as in claim 5, further including: scanning said flash memory array for a row to be refreshed;   erasing said row to be refreshed in said flash memory array;   programming said row to be refreshed in said flash memory array; and   incrementing an address of said row to be refreshed in said flash memory array.   
     
     
       7. A method of operating a flash memory array as in claim 2, wherein said erasing a selected row and said programming said selected row are performed after said incrementing. 
     
     
       8. A method of operating a flash memory array as in claim 2, wherein said erasing a selected row and said programming said selected row are performed between said erasing said row and said programming said row. 
     
     
       9. A method of operating a flash memory array as in claim 2, wherein said erasing a selected row and said programming said selected row are performed between said programming said row and said incrementing. 
     
     
       10. A method of operating a flash memory array as in claim 1, wherein after said scanning and prior to said erasing said method further includes storing an address of said row to be refreshed. 
     
     
       11. A method of operating a flash memory array as in claim 1, wherein after the said scanning and prior to said erasing said method further includes storing data from said row to be refreshed in a buffer. 
     
     
       12. A method of operating a flash memory array as in claim 11, wherein said programming act includes programming said data stored in said buffer in said storing data act. 
     
     
       13. A method of operating a flash memory array as in claim 5, wherein said selected bit indicates the address of a row to be refreshed. 
     
     
       14. A method of operating a flash memory array as in claim 5, wherein said first state is a programmed state. 
     
     
       15. A method of operating a flash memory array as in claim 6, wherein after scanning and prior to said erasing said method further includes storing an address of said row to be refreshed. 
     
     
       16. A method of operating a flash memory array as in claim 6, wherein after said scanning and prior to said erasing said method further includes storing data from said row to be refreshed in a buffer. 
     
     
       17. A method of operating a flash memory array as in claim 16, wherein after said scanning act and prior to said erasing act said method further includes storing an address of said row to be refreshed.